In a principal aspect the present invention relates to a pier construction for supporting structures in a soil matrix wherein the pier is formed with a special mechanical apparatus from an aggregate material by compacting successive lifts or sectors of the aggregate material located in a cavity in the matrix.
In U.S. Pat. No. 5,249,892, incorporated herewith by reference, a method and apparatus are disclosed for producing short aggregate piers in situ. The process includes forming a cavity in soil and then introducing successive layers of compacted aggregate material into the cavity to form a pier that can support a structure. The aggregate may be comprised of various materials. The lifts or layers of aggregate which are compacted during the pier forming process typically have a diameter of 1 to 3 feet and a vertical rise of similar dimension and range. Thus, such piers are made by drilling a hole or cavity in a soil matrix, placing aggregate or other select fill material in small discreet layers in the cavity, and then tamping each layer of the material in the cavity with a special mechanical tamper apparatus to provide impact or ramming energy to the layer of material. This apparatus and process produces a stiff and effective stabilizing element or pier. However, this method of pier construction has a limitation in terms of the depth to which the pier forming process can be accomplished economically. Typically the process described in the patent is limited to a depth of approximately 20 feet because of the equipment utilized, the time required to make a pier and the techniques that are available. Thus, there has developed a need for a mechanical apparatus, as well as a construction process, which can be successfully and economically utilized at greater depths yet have the attributes and benefits associated with the short aggregate pier method, apparatus and construction disclosed in U.S. Pat. No. 5,249,892.
Briefly, the present invention comprises a method for installation of a pier formed from layers of aggregate material in a soil matrix and includes the steps of positioning a hollow tube with a special mechanical bottom compacting apparatus in the soil matrix, removing the soil matrix from the core of the tube and the special mechanical bottom compacting apparatus followed by at least partially filling the tube and the special mechanical compacting apparatus with an aggregate material and then raising and lowering the tube and bottom apparatus within the soil matrix as the tube and bottom apparatus are incrementally raised in steps from the cavity. Raising and lowering of the tube and bottom apparatus enables a specially designed lower portion of the bottom apparatus to impact upon the aggregate material, thereby densifying the material, forcing the material laterally outward and simultaneously imparting lateral forces on the aggregate and the soil matrix and applying longitudinal forces on the aggregate. The tube with bottom apparatus may be vibrated while being incrementally raised and lowered depending upon conditions of the soil matrix and composition of the aggregate materials. The tube with bottom apparatus may also be pushed downward or driven downward during the xe2x80x9cloweringxe2x80x9d sequence to provide additional densification and lateral force energy. In this manner, compacted lifts are incrementally formed by the bottom apparatus as the tube is removed from the cavity in the soil matrix. The process is continuously repeated along the length of the soil cavity with a result that an elongate pier of separately compacted layers or lifts is formed within the soil matrix. A pier having a length or depth of fifty (50) feet or more can be constructed in this manner.
Numerous types of aggregate materials may be utilized in the practice of the process including a mixture of aggregate and dry cement. Such mixture has proven to be beneficial in creating a pier having significantly improved stiffness and integrity for support of a structure, especially when the soil matrix is very soft and weak.
The tube with bottom mechanical apparatus may be positioned within the soil matrix in the event the soil is soft by forcing the tube into the soil matrix with or without applying vibration energy. If the soil is hard, the soil matrix may be pre-drilled to form a cavity into which the tube apparatus is lowered or driven prior to filling the tube with aggregate. In any event, the soil contained within the hollow tube apparatus is removed from the tube apparatus once the tube apparatus is lowered, pushed, vibrated, driven or otherwise placed in the soil. A drill or other evacuation technique is used to remove the soil from the interior of the hollow tube apparatus. In soft soils, a removable cap or a sacrificial cap may be placed at the bottom of the hollow tube apparatus to prevent soil matrix from entering the tube. For such situations, removal of the soil matrix from within the hollow tube will not be necessary. Other steps described in the process of making the lateral displacement pier remain essentially the same. Other mechanical apparatus descriptions contained herein remain essentially the same.
In a preferred embodiment, the lower portion of the tube apparatus is designed with an inwardly extending bevel so that both lateral and longitudinal forces may be imparted to aggregate in the tube by the downward movement of the tube apparatus within the soil matrix cavity during incremental raisings and lowerings. The bevel may be effected by an internal thickening of material formed at the lower end of the tube apparatus. In that event, the drill or auger for removing the soil from the tube apparatus may have a special construction including reduced diameter section at the distal end of the drill or auger. The bevel may also be effected by an external thickening of material formed at the lower end of the tube apparatus. The bevel may also be effected by a combination of an internal thickening and an external thickening of material formed at the lower end of the tube apparatus.
During the practice of the method, the aggregate will be compacted and thus additional aggregate will necessarily be added to the tube apparatus as the aggregate is densified and compacted. Upon completion of the formation of the pier and total removal of the hollow tube apparatus from the soil matrix, the pier may be pre-loaded, for example, by placement of a static or dynamic load thereon, prior to placing a structure on the pier. This preloading process will stiffen the constructed aggregate pier and will cause prestressing and prestraining of the matrix soil in the vicinity of the pier, thus increasing the support capacity of the pier.
Thus, it is an object of the invention to provide a special hollow tube apparatus with a special designed bottom apparatus portion to create a compacted aggregate pier that extends to a greater depth and to provide an improved method for creating a pier that extends to a greater depth than typically enabled or practiced by prior short aggregate pier technology.
It is a further object of the invention to provide a method or process for installing a pier formed of aggregate material wherein the material has discrete compacted lifts along the length of the pier with the hollow tube apparatus and special designed bottom apparatus.
Yet a further object of the invention is to provide a method for forming an elongate pier having improved load bearing characteristics when incorporated in the soil matrix wherein the pier is formed of a compacted aggregate material and the compaction is effected by a hollow tube apparatus and special designed bottom apparatus which is placed within a soil cavity filled with the aggregate and may be vibrated, pushed downward, driven downward, or a combination of these.
Yet another object of the invention is to provide an improved method for forming a pier of aggregate material wherein the aggregate may be chosen from a multiplicity of options, including a mix of stone or other types of aggregate with dry cement.
Yet a further object of the invention is to provide an aggregate pier construction which is capable of being incorporated in many types of soil and which is further capable of being formed at greater depths than prior aggregate pier constructions.
These and other objects, advantages and features of the invention will be set forth in the detailed description which follows.